| Abbreviation | Definition |
|---|---|
| LY2 | The Large Commercial Yacht Code |
| LY3 | Large Yacht Code, Version 3 |
| M/S | Motor Ship |
| MCM | Mine Counter-Measures ship (Minesweeper) |
| MCMV | Mine Counter-Measures Vessel |
| MCS | Mine Countermeasures Ship |
| MEC | Medium Endurance Cutter |
| MFV | Motor Fishing Vessel |
| MGB | Motor GunBoat |
| MHA | MineHunter, Auxiliary |
| MLS | Missile Launching Ship |
| MM | Minelayer (Minecraft, Minelayer) |
| MMC | Coastal Minelayer (Minecraft, Minelayer, Coastal) |
| MMD | Destroyer Minelayer (Minecraft, Minelayer, Destroyer) |
| MMF | Fleet Minelayer (Minecraft, Minelayer, Fleet) |
| MOU | mobile offshore unit |
| MOW | Man-O-War |
| MPS | Maritime Pre-Positioning Ship |
| MRV | Multi Role Vessel |
| MS | merchant ship |